The fact is that the form of government that they came up with was unable to end slavery without a war. It was unable to end Jim Crow and second class citizenship until sometime in the last 50ish years. It is exceptionally difficult to change as you point out with regards to the ERA.
The landed white men were the ruling class in the US. They retained their status and for the most part still do. So, they weren't at all for freedom for all, or liberty for all. And that is my point, we can't look to them or the government as they created as a beacon to head towards to find freedom and liberty because it is not there. It was there for a minority of the population but given that today we generally view people other that landed white men as humans deserving of equal protection, we need to look at them and their documents according to what they were. You can call that presentism or whatever, I call it logical.
The proof is in the pudding. A person in Wyoming has far more electoral power than one in Cali. That power is flexed in the form of the Supreme court and unequal representation for the chief executive and Senate. We are still paying for this founding father planned inequity. It's a shitty way to do business to value some humans over others, but that is the case still today. It's how the system was created and how it remains. It remains that way in part because people buy the freedom and liberty bullshit that was written and look past what the actual outcome was. So people are stupid enough to deify Jefferson et al. to the detriment of reason. They created a system that was difficult to change, distrustful of the majority and did not live up to the words that they themselves used to describe it. It's a fairytale.
And so that is my big issue with "originalism". We aren't in 1780 and our issues are different. We can't look to 1780 humans to solve 2023 problems. They don't share present day values unless you value unequal representation, slavery and women as second class citizens. They could not foretell the future. That isn't judging Jefferson and his buddies by todays standards, it's frustration that we can't govern today by todays standards because people think that the standards of 1780 are superior.